This invention relates to a micro etching method and a system suited for highly selective etching of each layer of a multilayered LSI using a focused beam.
The sample micro etching method used in conventional focused ion beam working apparatuses such as a photomask repair system or an ion micro analyzer (IMA) is a sputtering etching method to sputter atoms from each sample by ion beam irradiation.
FIG. 2 shows the basic configuration of conventional focused ion beam working apparatuses. Ion beam 2 extracted from ion source 1 is focused by focusing lens 4, and irradiated onto sample 10 for sputtering etching. A chemical vapor deposition (CVD) gas is supplied onto the sample via nozzle 16 simultaneously with ion beam irradiation for local film forming. The ion beam is turned ON or OFF by blanking controller 12 and the ion beam deflection is controlled by deflecting controller 13. Secondary electrons or ions generated from sample 10 by ion beam irradiation are detected by secondary particle detector 9 (for example, a microchannel plate), and a scanning ion microscope (SIM) image is produced. This SIM image can be used for surface observation of the sample. Japanese Patent Laid-Open 245553/1986 is associated with such focused ion beam working apparatuses.
In FIG. 2, reference numeral 3 denotes an extracting electrode, 5 a beam limiting aperture, 6 a blanking electrode, 7 a blanking aperture, 8 a deflecting electrode, 11 a stage, 14 a valve, 15 a CVD gas cylinder, 17 a chamber, and 18 an all system controller.
Japanese Patent Laid-Open 13176/1982 is associated with a sample etching method, different from the simple sputtering etching method, which uses a chemical reaction by a reactive beam consisting of an ionized reactant gas. Japanese Patent Laid-Open 13177/1982 is associated with another etching method, which uses a chemical reaction generated when a focused ion beam is irradiated onto a sample in a reactant gas atmosphere.
U.S. Pat. Nos. 4503329 and 4609809 and U.S. Patent Application Ser. No. 32753 are associated with direct etching by a focused beam but do not contain reactive etching.
At present, semiconductor devices such as LSIs use multilayered conductors or devices to achieve high integration and sophisticated performance. There is an increasing demand that, when etching multilayered LSIs, which are highly dense in the vertical direction and have overlapped uneven layers, the etching can be stopped at a specified layer without causing damage to the lower layers.
There is another increasing demand that, for LSI design debugging and production process error analyses, the circuit repair time can be minimized by directly disconnecting or connecting LSI conductors by local etching. Such circuit repair requires etching at several tens locations of a LSI. Consequently, high speed etching and a high yield of about 100% are required.
Problems on etching of multilayered LSIs, which are imposed on conventional focused ion beam working apparatuses using the simple sputtering etching method, are as follows:
(1) The etching speed is almost proportional to the beam current. To produce a fine beam, however, high speed etching cannot be done because the beam current is restricted.
(2) The etching selectivity for the workpieces material is low, so that it is difficult to stop etching at the specified layer of a multilayered LSI because each layer of the LSI is etched at a uniform speed.
(3) The etching speed on an inclined face is high, so that the etched hole bottom is easily flattened and accurate etching along each uneven layer of a multilayered LSI cannot be done, causing damage partially to the under layer.
Etching by a chemical reaction between reactant gas molecules and a workpiece, such as reactive ion etching (RIE), can provide an extremely high etching speed, which is several tens fold of the sputtering etching speed, by increasing the reaction probability by gas pressure or ion energy. Use of an appropriate reactant gas enhances the etching selectivity of the etched layer to the under layer and provides accurate etching which causes no damage to the uneven under layer.
Japanese Patent Laid-Open 13176/1982 and Japanese Patent Laid-Open 13177/1982 are associated with systems which perform chemically reactive etching locally on a workpiece by using a reactant gas and a focused ion beam. The systems are designed to select a reactant gas according to a combination of the material of a special workpiece and that of its substrate and to etch selectively only one upper layer of the workpiece. On the other hand, the inventors of the present invention consider that, for example, in the case of a workpiece consisting of a laminate of Al conductor layers, SiO.sub.2 layers, Si.sub.3 N.sub.4 layers and the like, the layer to be etched and the under layer change by etching and an optimum reactant gas should be selected and supplied sequentially. For that purpose, changes of each etched layer should be exactly detected and reactant gases should be able to be efficiently selected and supplied in a short time. The systems mentioned above give no consideration to such problems, and accurate etching of multilayered LSIs is impossible.